Support DNS recursion and TCP queries

command/agent/command.go

@@ -52,6 +52,7 @@ func (c *Command) readConfig() *Config {
 		"address to bind RPC listener to")
 	cmdFlags.StringVar(&cmdConfig.DataDir, "data", "", "path to the data directory")
 	cmdFlags.StringVar(&cmdConfig.Datacenter, "dc", "", "node datacenter")
+	cmdFlags.StringVar(&cmdConfig.DNSRecursor, "recursor", "", "address of dns recursor")
 	cmdFlags.BoolVar(&cmdConfig.Server, "server", false, "run agent as server")
 	cmdFlags.BoolVar(&cmdConfig.Bootstrap, "bootstrap", false, "enable server bootstrap mode")
 	if err := cmdFlags.Parse(c.args); err != nil {
@@ -148,7 +149,8 @@ func (c *Command) setupAgent(config *Config, logOutput io.Writer, logWriter *log
 	}
 
 	if config.DNSAddr != "" {
-		server, err := NewDNSServer(agent, logOutput, config.Domain, config.DNSAddr)
+		server, err := NewDNSServer(agent, logOutput, config.Domain,
+			config.DNSAddr, config.DNSRecursor)
 		if err != nil {
 			agent.Shutdown()
 			c.Ui.Error(fmt.Sprintf("Error starting dns server: %s", err))

command/agent/config.go

@@ -30,6 +30,10 @@ type Config struct {
 	// DNSAddr is the address of the DNS server for the agent
 	DNSAddr string
 
+	// DNSRecursor can be set to allow the DNS server to recursively
+	// resolve non-consul domains
+	DNSRecursor string
+
 	// Domain is the DNS domain for the records. Defaults to "consul."
 	Domain string
 
@@ -154,6 +158,9 @@ func MergeConfig(a, b *Config) *Config {
 	if b.DNSAddr != "" {
 		result.DNSAddr = b.DNSAddr
 	}
+	if b.DNSRecursor != "" {
+		result.DNSRecursor = b.DNSRecursor
+	}
 	if b.Domain != "" {
 		result.Domain = b.Domain
 	}

command/agent/dns.go

@@ -19,36 +19,45 @@ const (
 // DNSServer is used to wrap an Agent and expose various
 // service discovery endpoints using a DNS interface.
 type DNSServer struct {
-	agent      *Agent
-	dnsHandler *dns.ServeMux
-	dnsServer  *dns.Server
-	domain     string
-	logger     *log.Logger
+	agent        *Agent
+	dnsHandler   *dns.ServeMux
+	dnsServer    *dns.Server
+	dnsServerTCP *dns.Server
+	domain       string
+	recursor     string
+	logger       *log.Logger
 }
 
 // NewDNSServer starts a new DNS server to provide an agent interface
-func NewDNSServer(agent *Agent, logOutput io.Writer, domain, bind string) (*DNSServer, error) {
+func NewDNSServer(agent *Agent, logOutput io.Writer, domain, bind, recursor string) (*DNSServer, error) {
 	// Make sure domain is FQDN
 	domain = dns.Fqdn(domain)
 
 	// Construct the DNS components
 	mux := dns.NewServeMux()
 
-	// Setup the server
+	// Setup the servers
 	server := &dns.Server{
 		Addr:    bind,
 		Net:     "udp",
 		Handler: mux,
 		UDPSize: 65535,
 	}
+	serverTCP := &dns.Server{
+		Addr:    bind,
+		Net:     "tcp",
+		Handler: mux,
+	}
 
 	// Create the server
 	srv := &DNSServer{
-		agent:      agent,
-		dnsHandler: mux,
-		dnsServer:  server,
-		domain:     domain,
-		logger:     log.New(logOutput, "", log.LstdFlags),
+		agent:        agent,
+		dnsHandler:   mux,
+		dnsServer:    server,
+		dnsServerTCP: serverTCP,
+		domain:       domain,
+		recursor:     recursor,
+		logger:       log.New(logOutput, "", log.LstdFlags),
 	}
 
 	// Register mux handlers, always handle "consul."
@@ -56,15 +65,25 @@ func NewDNSServer(agent *Agent, logOutput io.Writer, domain, bind string) (*DNSS
 	if domain != consulDomain {
 		mux.HandleFunc(consulDomain, srv.handleTest)
 	}
+	if recursor != "" {
+		mux.HandleFunc(".", srv.handleRecurse)
+	}
 
-	// Async start the DNS Server, handle a potential error
+	// Async start the DNS Servers, handle a potential error
 	errCh := make(chan error, 1)
 	go func() {
 		err := server.ListenAndServe()
-		srv.logger.Printf("[ERR] dns: error starting server: %v", err)
+		srv.logger.Printf("[ERR] dns: error starting udp server: %v", err)
 		errCh <- err
 	}()
 
+	errChTCP := make(chan error, 1)
+	go func() {
+		err := serverTCP.ListenAndServe()
+		srv.logger.Printf("[ERR] dns: error starting tcp server: %v", err)
+		errChTCP <- err
+	}()
+
 	// Check the server is running, do a test lookup
 	checkCh := make(chan error, 1)
 	go func() {
@@ -93,6 +112,8 @@ func NewDNSServer(agent *Agent, logOutput io.Writer, domain, bind string) (*DNSS
 	select {
 	case e := <-errCh:
 		return srv, e
+	case e := <-errChTCP:
+		return srv, e
 	case e := <-checkCh:
 		return srv, e
 	case <-time.After(time.Second):
@@ -119,10 +140,14 @@ func (d *DNSServer) handleQuery(resp dns.ResponseWriter, req *dns.Msg) {
 	m.SetReply(req)
 	m.Authoritative = true
 	d.addSOA(d.domain, m)
-	defer resp.WriteMsg(m)
 
 	// Dispatch the correct handler
 	d.dispatch(req, m)
+
+	// Write out the complete response
+	if err := resp.WriteMsg(m); err != nil {
+		d.logger.Printf("[WARN] dns: failed to respond: %v", err)
+	}
 }
 
 // handleTest is used to handle DNS queries in the ".consul." domain
@@ -147,7 +172,9 @@ func (d *DNSServer) handleTest(resp dns.ResponseWriter, req *dns.Msg) {
 	txt := &dns.TXT{header, []string{"ok"}}
 	m.Answer = append(m.Answer, txt)
 	d.addSOA(consulDomain, m)
-	resp.WriteMsg(m)
+	if err := resp.WriteMsg(m); err != nil {
+		d.logger.Printf("[WARN] dns: failed to respond: %v", err)
+	}
 }
 
 // addSOA is used to add an SOA record to a message for the given domain
@@ -353,3 +380,40 @@ func (d *DNSServer) serviceSRVRecords(dc string, nodes structs.ServiceNodes, req
 		resp.Extra = append(resp.Extra, aRec)
 	}
 }
+
+// handleRecurse is used to handle recursive DNS queries
+func (d *DNSServer) handleRecurse(resp dns.ResponseWriter, req *dns.Msg) {
+	q := req.Question[0]
+	network := "udp"
+	defer func(s time.Time) {
+		d.logger.Printf("[DEBUG] dns: request for %v (%s) (%v)", q, network, time.Now().Sub(s))
+	}(time.Now())
+
+	// Switch to TCP if the client is
+	if _, ok := resp.RemoteAddr().(*net.TCPAddr); ok {
+		network = "tcp"
+	}
+
+	// Recursively resolve
+	c := &dns.Client{Net: network}
+	r, rtt, err := c.Exchange(req, d.recursor)
+
+	// On failure, return a SERVFAIL message
+	if err != nil {
+		d.logger.Printf("[ERR] dns: recurse failed: %v", err)
+		m := &dns.Msg{}
+		m.SetReply(req)
+		m.SetRcode(req, dns.RcodeServerFailure)
+		resp.WriteMsg(m)
+		return
+	}
+	d.logger.Printf("[DEBUG] dns: recurse RTT for %v (%v)", q, rtt)
+
+	// Seems to be a bug that forcing compression fixes...
+	r.Compress = true
+
+	// Forward the response
+	if err := resp.WriteMsg(r); err != nil {
+		d.logger.Printf("[WARN] dns: failed to respond: %v", err)
+	}
+}

command/agent/dns_test.go

@@ -11,7 +11,8 @@ import (
 func makeDNSServer(t *testing.T) (string, *DNSServer) {
 	conf := nextConfig()
 	dir, agent := makeAgent(t, conf)
-	server, err := NewDNSServer(agent, agent.logOutput, conf.Domain, conf.DNSAddr)
+	server, err := NewDNSServer(agent, agent.logOutput, conf.Domain,
+		conf.DNSAddr, "8.8.8.8:53")
 	if err != nil {
 		t.Fatalf("err: %v", err)
 	}
@@ -173,3 +174,26 @@ func TestDNS_ServiceLookup(t *testing.T) {
 		t.Fatalf("Bad: %#v", in.Extra[0])
 	}
 }
+
+func TestDNS_Recurse(t *testing.T) {
+	dir, srv := makeDNSServer(t)
+	defer os.RemoveAll(dir)
+	defer srv.agent.Shutdown()
+
+	m := new(dns.Msg)
+	m.SetQuestion("apple.com.", dns.TypeANY)
+
+	c := new(dns.Client)
+	c.Net = "tcp"
+	in, _, err := c.Exchange(m, srv.agent.config.DNSAddr)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	if len(in.Answer) == 0 {
+		t.Fatalf("Bad: %#v", in)
+	}
+	if in.Rcode != dns.RcodeSuccess {
+		t.Fatalf("Bad: %#v", in)
+	}
+}